148 



WILLIAM L. DOLLEY, JR, 



Table 1 shows that when the illumination in the two beams 

 was equal the average angle made by 11 butterflies was +0.78 

 degrees, indicating that the butterflies tended to move in general 

 toward a point halfway between the two sources of light; and 

 that when the illumination in one beam was greater than that in 



TABLE i 



Orientation in continuous light from two sources. The numbers indicate the degree 

 of deflection from a line bisecting the 90 degree angle between the two beams. "Plus," 

 deflection toward right beam. If beams are of unequal illumination the stronger 

 one is to the right of the insect. "Minus," deflection toward other beam 



the other they moved toward a point nearer the source of stronger 

 light. This conclusion is evident from a comparison of the total 

 average angles made in beams differing in relative illumination. 

 The only apparent exception is the average angle made in two 

 beams one of which was three-fourths as strong as the other. 

 Although the total average angle made by all of the butterflies 

 in this test was only 0.28 degrees, 63.6 per cent or 7 out of the 

 11 animals tested under the two conditions, first, in two beams 

 of equal illumination and second, in two beams, one three-fourths 



